1. Field of the Invention
The present invention relates to the stabilization of polyoxyalkylene polyether polyols and the use of the stabilized polyols in the preparation of polyurethane foam. In particular the invention relates to stabilization of polyols with certain liquid stabilizer compositions and the color or scorch inhibition of flexible and semiflexible polyurethane foams made from the stabilized polyols.
2. Background and Related Art
Prior art methods for the stabilization of polyalkylene polyether polyols with antioxidants or stabilizers and the use of stabilized polyols in the preparation of polyurethane foams to inhibit scorch are well known.
U.S. Pat. Nos. 3,567,664 and 3,637,865 disclose polyurethane foams stabilized with a mixture of 2,6-di-tert-butyl-4-methyl phenol [butylated hydroxy toluene (BHT)] and p,p'-dialkyldiphenylamines. U.S. Pat. No. 4,010,211 teaches the addition of phenothiazine to a BHT/p,p'-dialkyldiphenylamine mixture. U.S. Pat. No. 4,794,126 discloses flame-retardant polyurethane foams stabilized with a combination of a diarylarylenediamine reaction product of diarylamine and alkyl ketone and a hindered phenol, specifically 3,6'-di-tert-butyl-4-sec-butyl phenol.
The stabilizers of the aforementioned prior art are solids and are generally dissolved in the polyol media by heating. To remove any undissolved stabilizer solids, the entire voluminous polyol mass is subject to a filtration step, after which the polyol precursor can be cured to the final foam product.
Statton, in "Evaluation of Hindered Phenols for Minimization of Foam Discoloration Using the Microwave Scorch Test" in J. CELLULAR PLASTICS, 346 (1984) studied four phenols in combination with the solid antioxidant p,p'-dioctyldiphenylamine alone and in the presence of phenothiazine. Although systems containing the BHT hundred phenol were fairly effective polyol stabilization packages, systems comprised of 2,6-di-tert-butyl-4-sec-butylphenol and p,p'-dioctyldiphenylamine did not provide satisfactory scorch resistance. In the Statton systems described, the amine appeared to be more effective in reducing scorch than the phenolic antioxidant. Even at maximum concentrations, this combination would not provide good scorch resistance in the polyols used.
U.S. Pat. No. 4,933,374 discloses polyoxyalkylene polyether polyol Compositions protected against oxidative degradation with a stabilizing amount of a synergistic mixture of 2,6-di-tert-butyl-4-sec-butyl phenol and a reaction product of diisobutylene, styrene, and diphenylamine wherein the weight ratio of the diisobutylene to the styrene is from about 2:1 to 5:1.
It would therefore be advantageous to have a liquid system of polyol stabilizers which are soluble in the polyol media at ambient temperatures. Two steps of the conventional process could therefore be eliminated, i.e., the dissolution of the stabilizer in the polyol media by heating and removal of the undissolved stabilizer solids by filtration. Serendipitously, additional advantages of liquid stabilizer compositions are their ability to be added to the polyol by metering or pumping which result in added convenience and safety.